1. Technical Field
The present invention relates to a data reading apparatus for an optical card which reads the optical card having a data area formed by aligning a plurality of data tracks each of which consists of a plurality of data bits along a reference line extending perpendicular to the data tracks.
2. Background Art
A data recording area 2 of an optical card 1 (FIGS. 9 and 10) has a plurality of bands 5. (FIGS. 5 and 8.) Each of the bands 5 is formed by vertically aligning data tracks 4, each of which is a row of data bits 3, as shown in FIG. 8. At the left side of the band 5 as viewed in FIG. 8 is provided two reference lines 6a which serve as the reference lines when the data bits 3 are detected. A reference numeral 6b denotes reference lines for a subsequent band 5.
When data on such an optical card 1 is to be read, a light 8, e.g., an infrared ray, emitted from an LED 7 is gathered, and the gathered light is irradiated onto the optical card 1, as shown in FIGS. 9 and 10 A light 9 reflected by the optical card 1 is received by an image sensor, such as a CCD line sensor 10. The data bits formed on the surface of the optical card 1 are sent through a decoder 11 to a CPU 12 where they are read.
Viewing of the card from the CCD line sensor 10 is regarded the same as viewing the card 1 through a slit 13 shown in FIG. 4. Scanning of the portion of the card 1 shown by the slit 13 from the left to the right produces a reading signal shown in FIG. 8. I/O of data is determined from the reading signal by determining the presence or absence of the data bit 3.
In a practical data reading operation, scanning of one data track 4 is repeated a plurality of times. In each scanning, a binary signal is read with the detection signal of reference lines 6a as a reference. Hence, in order to accurately read out the data recorded on the optical card 1, the reference lines 6a for the data track 4 must be stably detected and synchronized with data clocks. Various techniques have therefore been proposed including the PLL technique.
However, in the conventional data reading apparatus, in a case where data is separated using data clocks, synchronization of the data with the data clocks requires adjustment of magnification of an optical system.
Furthermore, in a case where the data clock components are extracted from the reading signal using the PLL technique, the reading signal is partitioned by the scanning periods of the sensor, and the phase thereof is not continuous, necessitating provision of synchronization bits to resynchronize the data clocks for each scanning. However, provision of synchronization bits decreases the recording capacity of the optical card 1.
Furthermore, in a case where data is read with a reference line 6a detecting signal as a reference, if the reference lines 6a are damaged or soiled, an accurate detection signal cannot be obtained, or detection signal cannot be obtained at all. These make provision of accurate data clocks and normal reading of the data bits impossible.